1. Field of the Invention
This invention relates generally to the field of nanoencapsulation. More specifically, the invention relates to a method of delivering phototherapeutic materials.
2. Background of the Invention
Photosensitive compounds such as indocyanine green (ICG) have been extensively studied as a basis for various medical treatments. These compounds can convert absorbed light energy to produce heat and chemical species, forming the bases for phototherapeutic (e.g. photothermal and photodynamic) treatments. Specific applications under investigation include laser tissue welding and treatment of skin diseases and cancers. There are several problems that limit the development of photosensitive compounds for new phototherapy applications. First, the pharmacokinetics of the photosensitive compound may be extremely fast. For example, ICG clears rapidly from the circulatory system with a half-life of 3-4 min, followed by a much slower clearance rate characterized by a half-life of 1+ hr. Second, certain photosensitive compounds have complicated solution behaviors due to their amphiphilic nature. They may have a tendency to aggregate in water depending on their concentration (bathochromically shifting absorbance characteristics of the compounds and reducing their fluorescence quantum efficiency) and may bind nonspecifically to human serum albumin, lipoproteins, plasma proteins, and endothelial cells. Some photosensitive compound solutions are unstable as the photosensitive compound undergoes thermal degradation and photodegradation.
The preparation of colloidal carriers for photosensitive compounds has been studied to address the issues of fast blood clearance and uncontrolled protein binding. Emulsions, like a phospholipid-stabilized oil-in-water system and a lecithin-stabilized commercial product called Intralipid, are one such material. It has been reported that blood clearance time may be lengthened but that the instability of the emulsion structure led to photosensitive compound leakage. Polymeric particles have recently been studied as another photosensitive compound carrier. Polymeric hollow spheres containing light-responsive dyes or nanoparticles may be prepared through a technique called layer-by-layer assembly. Among this technique's drawbacks are the numerous steps in their preparation and encapsulation, and capsule deformation upon drying due to their thin nm-scale shells.
Consequently, there is a need for simple methods and compositions for phototherapeutic treatments which prevent photosensitive compound leakage and also provide for repeated treatments.